The present invention relates to a tunnel administration technique used when a remote terminal connects through a tunnel to the server in a remote access network.
Efforts are continuing to develop a form of connection for a remote terminal of a business corporation to access the server of its own corporation through connection service by a Internet Service Provider (ISP). This access method, though it requires the use of a network built by another company, enables the business firm to use the network in the same way as it uses its own network, and therefore it is called a Virtual Private Network (VPN). A form of connection by which to connect LANs of branch offices through the Internet is a typical example of the VPN.
Tunneling is one of techniques for building a VPN. Tunneling is a technique that uses an intermediate network as a tunnel. When data based on a certain protocol is carried by an intermediate network, it is encapsulated beforehand so as not to have to worry about dealing with another network of a different protocol and when the data gets out of the intermediate network, the data is decapsulated and sent on another network of the same protocol as the network it started its journey on. For example, if a Wide Area Network (WAN) on which a VPN is built is the Internet, an IP (Internet Protocol) packet is encapsulated by adding an IP header to it to pass through the WAN.
As tunneling protocols, L2TP (Layer 2 Tunneling Protocol), PPTP (Point-to-Point Tunneling Protocol) and L2F (Layer-2 Forwarding) are well known.
In recent years, mobile computing by a portable telephone or a wireless LAN has been used widely, and the subscribers are on a steady increase. With scarcity of IPv4 (Internet Protocol version 4) addresses, it has become a general trend to use private addresses in the IP network within the firm (a private LAN). For this reason, in order to access a private LAN from a mobile terminal, it is necessary to build a so-called VPN of a structure such that a tunneling function is provided at the outlet (gateway) of a mobile communications network and at the access server of a private LAN and thus it appears as if those two points were connected by a private line through the networks between them.
However, the tunneling protocol used in the VPN specifies only a method for forming a tunnel and so on, but it does not provide any detailed specification for communication line control.